The National Institute of Child Health and Human Development is participating in a study of the analyses of the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC), of specific hospital admissions, and of the Confidential enquiry into Still births and Deaths in Infancy (CESDI) in order to (1) correlate changes in sleep position with the health and developmental outcomes of a population of infants; and (2) to determine whether changes in SIDS rates correlate in time and extend with a change in infant sleep position.